Rollup merge of #126013 - nnethercote:unreachable_pub, r=Urgau

Add `#[warn(unreachable_pub)]` to a bunch of compiler crates

By default `unreachable_pub` identifies things that need not be `pub` and tells you to make them `pub(crate)`. But sometimes those things don't need any kind of visibility. So they way I did these was to remove the visibility entirely for each thing the lint identifies, and then add `pub(crate)` back in everywhere the compiler said it was necessary. (Or occasionally `pub(super)` when context suggested that was appropriate.) Tedious, but results in more `pub` removal.

There are plenty more crates to do but this seems like enough for a first PR.

r? `@compiler-errors`

compiler/rustc_codegen_llvm/src/debuginfo/create_scope_map.rs

@@ -15,7 +15,7 @@ use crate::llvm::debuginfo::{DILocation, DIScope};
 
 /// Produces DIScope DIEs for each MIR Scope which has variables defined in it.
 // FIXME(eddyb) almost all of this should be in `rustc_codegen_ssa::mir::debuginfo`.
-pub fn compute_mir_scopes<'ll, 'tcx>(
+pub(crate) fn compute_mir_scopes<'ll, 'tcx>(
     cx: &CodegenCx<'ll, 'tcx>,
     instance: Instance<'tcx>,
     mir: &Body<'tcx>,